Pregnancy Rate after Frozen/Thawed Blastocysts Transfer vs. Blastocysts Cultured from Thawed Cleavage Embryos

Introduction:
Fresh blastocysts (BLTs) result in better pregnancy rates (PR) compared with cleavage embryos. Few studies are available to determine if the same implies for thawed blastocysts/cleavage embryos. Fewer studies address the issue: Is transfer of thawed blastocysts superior to the transfer of blastocysts cultured from thawed cleavage embryos (TCE’s).

Aim:
To compare PR after thawed blastocyst transfer with PR after blastocysts cultured from TCE’S, and evaluate the preferable method.
Methods:
Retrospective analysis of all FET cycles between 01.01.2015 and 31.12.2017 at the Galilee Medical Center, Nahariyah. PR with thawed BLT (group A) was compared to PR with BLTs cultured from day 3 TCE’s (group B). Both groups were compared with PR from day 3 TCE’s (group C). Statistical analysis was performed using chi square test.

Results:
A total of 448 frozen/thawed cycles were performed resulting in 417 ET’s. In group A (61 cycles) 10 (16%) had positive pregnancy test (PPT) yielding 9 (15%) clinical pregnancies (CP’s). In group B (40 cycles), 15 (38%) had PPT yielding 12 (30%) CP’s. In group C (214 cycles), 57 (27%) had PPT yielding 42(20%) CP’s. Group B compared with group A had higher CP rate with borderline statistical significance (P=0.056) and significantly higher PPT’s (P<0.02), Group B CP rate tended to be higher compared with group C but did not reach statistical significance (P=0.069).

Conclusion:
BLT’s cultured from TCE’S may result in higher PR compared with thawed BLT’s and day 3 TCE’s. Further studies with larger groups are needed to establish these conclusions.